Micromixing using a conductive liquid-based focused surface acoustic wave (CL-FSAW)

Acoustic manipulation of fluids and particles has gained much attention in microfluidics, owing to its advantages of non-invasive manipulation and low power consumption. Microchannel mixing has been limited to diffusion-based mixing, because of low Reynolds number that has a low mixing efficiency. In this study, we firstly introduce a conductive liquid-based focused surface acoustic wave (CL-FSAW) device for mixing. Using the concentrated acoustic force of CL-FSAW, rapid and efficient mixing of deionized water and fluorescent particle suspension was demonstrated in a microfluidic channel. Effects of the applied voltage and the flow rate on the mixing efficiencies were investigated. As the flow rate decreased or the applied voltage increased, the mixing efficiency increased. At 21 V, mixing efficiencies were higher than 90% at a flow rate lower than 120 μL min⁻¹. In addition, our device was applied to silver nanoparticle synthesis at the optimal mixing condition (100 μL min⁻¹ and 21 V).